1. Field of the Invention
The present invention relates generally to a manipulator, and its control device and method. More specifically, the invention relates to a medical manipulator operative in a master/slave mode, and its control device and method.
2. Related Background Art
In conventional laparoscope surgery such as laparoscopic cholecystectomy, an endoscope and forceps are inserted into an abdominal cavity through trocars set in small incisions made in the abdomen of a patient. Then, an operator conducts operation while watching the image acquired by the endoscope on a monitor. Since this type of operation does not need to open the abdomen, physical burden on the patient is alleviated, and the time required for recovery and discharge from the hospital after operation is greatly reduced. Therefore, its adaptation to wider fields of application is expected. Conventional laparoscope surgery, however, involves some problems. That is, the operator cannot directly observe the affected part of the patient. Additionally, there are used forceps only having an opening/closing gripper, not convenient to control and therefore unsuitable for surgery. Thus, the conventional laparoscope surgery needs high skills of operators.
To cope with these problems, it has been studied and is now being employed to furnish the forceps end with some degrees of freedom of motion so that a work unit (slave unit) at the forceps end having a plurality of degrees of freedom works in accordance with movements of a control unit (master unit) controlled by an operator to execute laparoscope surgery in a master/slave operative mode.
As one of master/slave medical manipulators, there is a remote-control device in which the master unit and the slave unit are normally located apart from each other. This is configured to set a plurality of slave arms on the patient and control positions and orientations of the medical manipulator's ends by controlling the master unit located apart from the patient. This system is complex and large-scaled, and needs high purchasing and maintenance costs. Moreover, it is not so convenient because of requiring much time to set the system ready for actual operation and being liable to interruption of operation. Furthermore, since the operator cannot attend closely to the patient during operation and is not available for quick treatment upon emergent accident, the system is insufficient from the viewpoint of safety.
There is another master/slave medical manipulator in which some of axes in the master unit and the slave unit are common axes. This is a simple, easy-to-employ, unitary medical master/slave manipulator. As compared with the foregoing remote-controlled manipulator, the operator can attend closely to the patient and directly controls the manipulator. Therefore, this unitary manipulator significantly reduces the problem of safety.
However, these medical manipulators have been developed mainly targeting their functions with affected parts to be operated or treated, and other issues remain unsolved, including how the system is easy to set in the operating room, easy for the operator to use, easy to sterilize and clean, easy to start its actual use, etc. as well as the issue of the cost.
One of problems of conventional techniques is that, if the master/slave medical manipulator is started to move from a status where the control unit (master unit) and the work unit (slave unit) do not coincide in orientation, the slave unit does not move as the user (operator) intends.
This is because, if the operator starts to control the manipulator from those both do not coincide in orientation, the operator cannot accurately recognize the difference between the orientation of the slave unit displayed on the endoscopic monitor and the orientation of the control unit and gets confused. Under the condition, the manipulator is unreliable in controllability and degrades in safety. Thus, it involves technical problems to be overcome.
To overcome those problems, there is a method of bringing the master unit into agreement with the orientation of the slave unit held stationary (Japanese Patent Laid-open No. JP-H08-215204A). This method is a diversion of a method having been employed in an industrial robot.
More specifically, in a manipulator having a detector means for detecting orientation angles of the slave portion and the master portion and a means for comparing results of their detection, while stopping the slave, the operator first controls and brings the master unit into agreement with the orientation of the slave, and thereafter starts the master/slave motion. However, this method fails to improve the controllability of the manipulator because the operator must conduct alignment of the orientations every time before starting or re-starting the master/slave motion. Moreover, since the operator must conduct the alignment for all of plural degrees of freedom of motion, it takes much time for the alignment. Furthermore, these problems cannot be disregarded also from the standpoint of quick attendance and treatment against unexpected accidents on site.
There is another method for automatically move the master unit into agreement with the orientation of the slave unit (Japanese Patent Laid-open No. JP-2002-053685). In this method, a manipulator includes a detector means for detecting orientation angles of the slave unit and the master unit and a means for sequentially comparing results of their detection. Then, the manipulator is operative in a transitional master/slave mode in which the slave is moved based on the difference between the orientation of the master unit and that of the slave unit as well as the time required for alignment of the orientations. This method removes the troublesome process of alignment, which is one of disadvantages of the foregoing method, and realizes the motion faithful to the operator's intention even during the alignment operation of orientations. However, if the alignment of orientations is started under existence of a large difference in orientation, then the distance of automatic movement of the slave unit and its time are large, and the slave unit starts moving in response to the alignment start command. Therefore, automatic motion out of the operator's intention appears saliently, and the safety issue still remains unsolved.